WASHINGTON, April 18 (Reuters) - The U.S. government will issue new natural gas pipeline safety rules this summer in hopes of reducing fatal accidents, which have more than doubled since 2008, a regulator said on Monday.

The death toll from pipeline safety accidents rose from 9 in 2008 to 13 in 2009 and reached 22 last year, said Transportation Secretary Ray LaHood.

To shore up safety, LaHood said, the U.S. Transportation Department, which oversees pipeline safety, will issue a rule in August requiring all natural gas pipeline operators to evaluate the risks of accidents on their systems from explosions, corrosion, leaks and other problems and take immediate steps to mitigate them.

"This is not acceptable," LaHood said of the rising death toll as the department kicked off off a day-long summit on pipeline safety.

"I'm deeply concerned about the rising number of deaths in pipeline explosions," he added, calling for government officials and companies to discuss better coordination after three major oil and natural gas pipeline accidents occurred in the last year.

A PG&E Corp (PCG.N) natural gas line exploded in a San Francisco suburb last September, killing eight people and destroying 37 homes.

In February, a natural gas explosion on a pipeline operated by UGI Utilities (UGI.N) killed five people in Allentown, Pennsylvania. Last year, an oil pipeline leak in the Midwest spilled thousands of barrels of crude.

A 2.5-million-mile network of pipelines crisscrosses the United States, carrying everything from crude oil to natural gas to refined products like gasoline and jet fuel.

Christopher Helms, CEO of NiSource Gas Transmission and Storage (NI.N) and head of the Interstate Natural Gas Association of America's pipeline safety task force, said the industry is already working to mitigate risks on older pipelines, such as to how establish and verify safe pressure levels.

Helms said the biggest risk for pipelines comes from excavation damage, which accounted for almost half of the reported pipeline incidents from 2002 to 2009.

"Risks such as corrosion and material flaws are the next most common cause for incidents," he said.

Legislation was introduced in the U.S. Senate in February that includes many of the pipeline safety improvements the administration is seeking. (Reporting by Tom Doggett; editing by Jim Marshall)